I just love when I'm very specific in searching for something that I get offers for my septic system to be pumped (don't have one) or photos of naked animals.
I think it's "Sa...." something. I find the coaches listed on the letterhead, but nothing like the one on the letter. It may be an assistant coach.
Now, if it was dated 1973, that was when they dumped their basketball coach and hired Thomas "Satch" Sanders.
I have some obscure autographs and found a website that specializes in identifying such, but didn't find mine. You could try googling that instead of the name. Or...have you thought of contacting Harvard and asking them? They have records going back to day one of the school's founding.